The present invention relates generally to fluid control devices. More particulary, the invention relates to a valve member for a valve of the ball valve type.
Ball valves manufactured from plastic material are known. These valves incorporate a rotatable plastic ball adapted to close off a thoroughbore. The ball has a central hole or aperture roughly equal to the thoroughbore of the valve. The ball is encapsulated between valve seats which comprise two ring seals mounted inside a valve body. The external surface of the ball has a part spherical shape around the area in contact with the seals. The spherical surface of the ball must not have any distortions and requires a high quality surface finish in order to achieve proper sealing.
In conventional plastic ball valves the ball is of a single configuration that is injection moulded. After moulding, the ball requires machining since it is virtually impossible to obtain a spherical shape of the external surface in the injection molding process. Frequently, there is an additional operation required to improve the surface finish of the external surface of the ball. Plastics used to produce the ball are often very expensive, because they must fulfil strict requirements of high wear resistance and low coefficient of friction. As a result the process of producing a plastic ball is inefficient and costly.
It is therefore an object of the invention to provide a new and improved ball or valve member for a valve of the ball valve type that has reduced manufacturing cost.
In accordance with the above objects and those that will be mentioned and will become apparent below, the ball valve member in accordance with this invention comprises a frame member having at least first and second sides and a flow passage therethrough, the frame member including a first set of attachment members disposed on the first side and a second set of attachment members disposed on the second side, at least first and second shells, the first shell including first engagement means adapted to engage the first set of attachment members, the second shell including second engagement means adapted to engage the second set of attachment members, a first sealing surface disposed on at least the first shell, and drive mechanism means adapted to engage the drive mechanism of a fluid control device to enable rotation of the ball valve in the fluid control device.
An advantage of this invention is that a ball valve member is made from only three components parts; two of which are identical. This makes the manufacture and assembly of the valve member relatively simple and inexpensive. Furthermore, each of the component parts can be replaced when damaged, instead of replacement of the whole unit as in the prior art devices.